Technology Why drilling for geothermal energy can cause earthquakes?

Why drilling for geothermal energy can cause earthquakes?

Geothermal wells in Vendenheim (Bas-Rhin). (FRANCK DELHOMME / MAXPPP)

Geothermal energy is renewable energy which can produce both electricity and heat. When it rains, water seeps into the ground and descends towards the center of the Earth, where it is warmer. A geothermal power station, using a set of communicating vessels, will send water into a borehole to bring warmer water from the basement up through another well. Going up, it turns into vapor. Arrived at the surface, in the power station, this vapor will turn an alternator to produce electricity. Or be used directly in a district heating network. You can even do both, it’s called cogeneration. In Vendenheim, near Strasbourg, the project was to supply between 15,000 and 20,000 homes with electricity and nearly 26,000 with heat.

Surface geothermal energy with heat pumps which are now used in thousands of homes is not a problem, since the pipes remain in the band of the first 200 m. The problem is revealed with the deep geothermal energy which descends between 1,500 m and 5,000 m: drilling and sending water under pressure can cause cracks in the Earth. It is therefore necessary to know the geology of the subsoil well to embark on such operations: either the drilling is very compact and there is not too much risk, or it is more fragmented and faults can cause the ground to move up to ‘on the surface.

The Parisian, Alsace and Aquitaine basins are the most suitable for deep geothermal energy. But there can be surprises. Today, nearly 90 countries use it to produce heat, cold, or electricity, and seismologists are watching closely the earthquakes induced by this technique. One of the most intense took place three years ago in South Korea. The city of Pohang, in the east of the country, was hit by an earthquake of 5.4 on the Richter scale. An earthquake that left 135 people injured and destroyed thousands of homes.

But geothermal energy is far from being the only or the first source of induced earthquakes; other activities also cause it, such as mining and the exploitation of shale gas and oil with the famous hydraulic fracturing.

France intends to double the share of geothermal heat by 2030 to reduce our CO2 emissions. The energy transition law plans to drop from 20% today to 38% in 2030. Replacing oil or gas boilers with geothermal energy is better for the climate. For 50 years, a million French households have already been supplied by deep geothermal energy, in Alsace, in the Paris basin, in particular the city of Ivry-sur-Seine … And the Maison de la radio, was the first installation in France to use this technology to produce part of its heating.

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